The invention relates to the known anodization technique of passing a fixed current through a semiconductor in the presence of hydrofluoric acid to create a structural change in the semiconductor material which remains single crystalline but becomes porous. The porous region may then be oxidized such that it becomes electrically insulative.
As shown in "Oxidized Porous Silicon Isolates Better Than Sapphire", Charles Cohen, Electronics, Jan. 27, 1981, pages 77-78, an entire lower substrate area of silicon beneath and around islands of single crystal silicon is anodized to a porous state, and then oxidized to dielectrically isolate the active elements to be formed in the islands. Anodization current is stopped at PN junctions and spreads laterally until it can exit between the islands.
The present invention utilizes anodization in a selective manner for pattern definition. Rather than anodizing a entire lower substrate, the present invention provides anodization only of long narrow vertical nocthes or grooves which separate regions and define patterns. The present technique is an alternative to traditional masking and etching.
The invention may provide oxidized or non-oxidized grooves. The invention may further afford a two step technique comprising anodization, followed by oxidation and removal etching, followed another anodization from the bottom of the groove, forming a deeper groove.